This application is based on and claims priority from Korean Utility Model Application No. 99-8668 filed on May 20, 1999, the contents of which are incorporated herein by reference.
(a) Field of the Invention
The present invention relates to a friction hinge device and, more particularly, to a clip type friction hinge device which can effectively control frictional volume with a minimized size.
(b) Description of the Related Art
Generally, a friction hinge device is to keep one rotating body at a predetermined position based on the frictional force working between the rotating body and a second body standing in a contact relation to the rotating body For instance, such a friction hinge device may be used for controlling screen angles of notebook computer monitors or for controlling the positions of sun-visors of automobiles. The frictional force working between the rotating body and the second body can be given with multiplication of the frictional volumes of the two bodies by the force applied to the rotating body in an axial direction.
In view of the ways of generating such a frictional force, there are various types of friction hinge devices. Among them, a wrap spring type where the frictional force is generated between a shaft and a spring wrapped around the shaft, a shaft disk compression type where a circular friction plate is mounted over the shaft, and a U-shaped clip type where a shaft is pressed against a multi-plated U-shaped spring have been extensively used.
In the wrap spring type, the processing steps may be simplified at a relatively lower cost. However, in such a type, the frictional force is determined depending upon the processing degree of the end portions of the spring. Thus, in order to make a high-quality friction hinge device, production cost should be increased. Furthermore, the amount of backlash is susceptible to the combination state of the end portions of the spring, and a separate support for supporting the shaft and the spring should be externally provided. This results in increased device size.
In the shaft disk compression type, it is easy to install a unit for controlling the force to be applied to the shaft in the axial direction. However, when the device size is decreased, the frictional volume is also decreased. Thus, it becomes impossible to use such a friction hinge device for a large torque application. Furthermore, leakage of lubricant is liable to occur, and hence, long-term durability of the device cannot be expected.
In contrast, in the U-shaped clip type, the frictional force is determined depending upon the number of the spring plates so that various kinds of friction hinge devices capable of producing large range of torque can be easily made.
FIG. 1 illustrates a U-shaped type friction hinge device according to a prior art. As shown in FIG. 1, the friction hinge device 100 includes a housing 130, and a U-shaped clip 110 held fixed within the housing 130. The U-shaped clip 110 is provided with first and second arms 112 and 114, and an empty portion 116 defined by the first and second arms 112 and 114. A shaft bar 120 is disposed at the empty portion of the U-shaped clip 110. The housing 130 may be fixed to a body of a notebook computer.
The clip 110 is pressed against the shaft bar 120 in the axial direction to thereby generate the required frictional force.
Specifically, when the shaft bar 120 contacting the clip 110 is forced to be rotated in a clockwise or an anti-clockwise direction, it does not rotate at the relatively early stage because the static frictional force working between the clip 110 and the shaft bar 120 is greater than the rotational force applied to the shaft bar 120. As the rotational force of the shaft bar 120 becomes so increased as to outweigh the static frictional force, the shaft bar 120 starts to be rotated.
When the shaft bar 120 is rotated by a predetermined angle and the rotational force applied thereto is released, the rotation of the shaft bar 120 is interrupted, and the shaft bar 120 is kept at that state due to the frictional force working between the shaft bar 120 and the clip 110.
However, in the above structured U-shaped clip type friction hinge device, there exist several problems like the below.
First, in order to generate the desired frictional force, the force applied to the shaft in the axial direction should be altered while not controlling the frictional volume. Therefore, the pressurizing force against the shaft is constantly maintained even at the relative rotation of the shaft and the U-shaped clip. In this situation, relatively large force should be required to operate the shaft, and the rotation of the shaft cannot be made in a fluent manner, resulting in abrasion of the friction interface.
Furthermore, since the shaft is in a fixed contact with the clip, the abrasion of the friction interface becomes so serious that the pressurizing force against the shaft is radically decreased. Consequently, the combination relation between the shaft and the clip becomes weak in a relatively short time interval, resulting in reduction in cycle life of the device.
In addition, as the clip has an empty portion and both end portions of the device are in an opening state, leakage of lubricant is liable to occur.
It is an object of the present invention to provide a friction hinge device which can freely control the friction volume while reducing the abrasion of the friction interface.
This and other objects may be achieved by a friction hinge device with a housing, and a torsion spring held fixed within the housing.
The torsion spring has an outer surface with a predetermined diameter, an inner surface differentiating in diameter, and a breakthrough hole defined by the inner surface. The outer surface of the torsion spring has a protrusion. The inner surface of the torsion spring is formed with a pair of first diameter portions facing to each other and second diameter portions disposed between the first diameter portions. The second diameter portion has a diameter greater than the diameter of the first diameter portion. The torsion spring is formed with a plurality of plate segments sequentially attached to each other.
The housing has an inner surface spaced apart from the outer surface of the torsion spring with a predetermined distance, and a groove for receiving the protrusion of the torsion spring in a tight manner.
A shaft bar is fitted into the breakthrough hole of the torsion spring such that a center portion of the shaft bar tightly contacts the first diameter portion of the torsion spring.
The friction hinge device may further include end caps provided within the housing at both sides of the torsion spring, bearings internally provided at side end portions of the housing to support the shaft bar, and friction plates fitted between the second diameter portions and the shaft bar such that the friction plates are pressed against the shaft bar.